The present invention relates to a seal between upper and lower halves of an inner compressor discharge case and particularly to a seal between the case halves tolerant of warpage during turbine operation.
In a turbine, e.g., a gas turbine, the compressor section includes a stationary inner barrel formed of two semi-cylindrical halves secured one to the other generally along a horizontal midline forming an annulus. The aft end of the inner barrel is secured to a compressor discharge casing which provides support for the nozzle support ring supporting the first-stage nozzle. The inner barrel, in part, segregates a high-pressure region external to the barrel from a lower pressure region within the barrel and about the rotor. The barrel halves at the horizontal midline have metal-to-metal contact surfaces which are machined to high tolerances in efforts to eliminate leakage after assembly and during use. However, warpage during operation of the turbine due to creep can leave a gap of approximately 5 to 7 mils at the bolted horizontal joints between the upper and lower halves of the inner barrel. As a consequence, leakage paths can and do appear between the halves of the inner barrel. A need has therefore arisen to minimize or eliminate any such leakage paths in a manner which is tolerant to warpage during turbine operation.
In accordance with a preferred embodiment of the present invention, there is provided a seal for application along the registering and joined horizontal margins of the halves of the inner compressor discharge case, i.e., the inner barrel, in a manner tolerant to warpage of the inner barrel during turbine operation. Particularly, grooves are machined along the margins of one of the upper and lower barrel halves and between the bolts at axially opposite ends of the one barrel half. The margins along the other barrel half are machined to form a sealing surface and are not provided with grooves. A composite tubular woven seal is provided in each of the grooves of the one barrel half and projects outwardly of the margin of each groove such that, upon joining the halves to one another along the mating margins, the composite tubular woven seal is compressed to compliantly seal against the machined surfaces of the margins of the other barrel half.
Particularly, the composite tubular woven seal is compliant as a result of the multiple layers forming the seal. The layers include an inner woven metal core, a fiber material, a metallic foil and a metal outer covering. Preferably, the inner metal core is formed of a woven stainless steel which is surrounded by a silica fiber. The fiber, in turn, is surrounded by a stainless steel metal foil and the outer covering is formed of a braided material, for example, Haynes 188. Because of the nature of the composite tubular woven seal, the seal is compliant, particularly as a result of the resiliency of the metal core and surrounding silica fiber. Moreover, the metal foil layer surrounding the fiber prevents leakage between the margins of the barrel halves, while the braided outer covering serves as a protective wear surface. The inner metal core and silica fibers tend to retain their generally circular configuration in cross-section such that the seal, when compressed between the margins of the barrel halves, is preloaded or biased for return to its circular cross-sectional configuration. In this manner, any leakage flow through gaps formed as a result of warpage during turbine operation are sealed by the composite tubular woven seal.
In a preferred embodiment of the present invention, there is provided an inner compressor discharge case for a gas turbine, comprising a cylindrical barrel formed of upper and lower halves joined to one another at margins thereof along a horizontal midline to form a pair of diametrically opposed joints along opposite sides of the barrel, each of the margins of one of the halves having a groove extending generally parallel to an axis of the cylindrical barrel, each of the margins of another of the halves having a sealing surface extending generally parallel to the axis of the cylindrical barrel, a compliant seal disposed in each of the grooves including a seal body formed of multiple layers of different materials for compliantly and sealingly engaging against the margin of another of the halves upon securing the halves to one another.